Release api_core 1.9.0 (#7671)

* Release 1.9.0
diff --git a/setup.py b/setup.py
index a36bede..9f2b988 100644
--- a/setup.py
+++ b/setup.py
@@ -22,7 +22,7 @@
 
 name = "google-api-core"
 description = "Google API client core library"
-version = "1.8.2"
+version = "1.9.0"
 # Should be one of:
 # 'Development Status :: 3 - Alpha'
 # 'Development Status :: 4 - Beta'